The present invention relates in general to semiconductors and, more particularly, to a semiconductor control circuit for an electromechanical device.
Linear actuators are electromechanical devices having a component that undergoes a linear displacement when a current is applied through a coil of the actuator. A typical bidirectional linear actuator includes a spring loaded piston surrounded by a solenoid coil. Pulse width modulated voltage pulses are applied across the coil with an H-bridge transistor network to induce a magnetic field with the coil current. The magnetic field displaces the piston a distance proportional to the average value of the coil current. The displacement is controlled by sensing and controlling the average current through the coil.
Prior art actuators sense the coil current by routing the coil current through two sense resistors, each coupled to an end of the H-bridge, and measuring the voltages across the resistors. Current is measured at the beginning and the end of each voltage pulse, where the coil current reaches maximum and minimum levels, and the average current is computed from these measurements. This method is reasonably accurate, but suffers from high cost due to the need for two external resistors and complex sensing circuitry to derive the average current value from the two measurements. Other prior art schemes use only one external resistor connected directly to the coil, but have low accuracy due to large common mode voltage swings across the resistor.
Hence, there is a need for an integrated circuit for controlling an electromechanical device that can detect the average coil current at a lower cost while maintaining high accuracy.